Image sensors can receive optical signals from objects and convert them into electrical signals, which can be transmitted for further processing, such as being digitalized, and stored in a storing device (for example, a memory, an optical disk or a magnetic disk), or displayed on a displayer. Image sensors are usually used in digital cameras, vidicons, scanners, fax machines and etc. Generally, there are two types of image sensors, including Charge Coupled Device (CCD) image sensors and Complementary Metal Oxide Semiconductor (CMOS) image sensors. Compared with a CCD image sensor, a CMOS image sensor features with higher integration level, less power consumption, lower production cost and etc.
With the image sensors getting smaller and smaller, and pads in the image sensors being more and more, distances between adjacent pads in image sensors become smaller, which brings more difficulty for packaging image sensors.
Among various existing packaging technologies of image sensor chips. Chip on Board (COB) packaging technology is more widely used. This is because a product packaged by the COB packaging technology normally has advantages of high reliability, high stability, high integration level, a small size, simple manufacturing processes, low package cost, and the product can be easily used.
Referring to FIG. 1, in a COB packaging process, an image sensor chip 31 is attached onto a circuit board 34 directly using an adhesive agent or a bonding method, such as automatic tape bonding, wire bonding or flip-chip bonding method. Then pads 32 on the image sensor chip 31 are electrically connected with connection points on the circuit board 34 by a wire bonding technology. During the COB packaging process, the image sensor chip 31 is not protected by a protection device, thus, an image sensing area 33 on the image sensor chip 31 is prone to be polluted or damaged.